7.5. Compact Conditional Syntax

Throughout this book we use statement blocks (statements surrounded by
curly braces) with all
conditional statements, even if a block
contains only one statement:

if (x == y) {
trace("x and y are equal");
}

For the sake of terseness, ActionScript does not require curly braces
when a conditional has only one substatement. A single substatement
may quite legitimately be placed directly after an
if or an else if statement
without any curly braces, like this:

if (x == y) trace ("x and y are equal");

Or like this:

if (x == y)
trace ("x and y are equal");

For some programmers, this style can be a little slower to read and
slightly more error prone, though it undeniably saves room in source
code.